Dispersion field

In 2152, the Torothans, who suspected the crew of the Enterprise NX-01 of collaborating with dissenter Zobral, activated an orbital dispersion field utilizing a series of artificial satellites, in order to prevent the crew from detecting anything on the surface below one hundred kilometers. Although the field covered approximately one half of one of the planet's continents, LieutenantReed managed to devise a plan whereby he could get clear readings by disabling three of the satellites. SubcommanderT'Pol, however, overruled this plan, believing that such an action would provoke the Torothans into taking aggressive actions against Enterprise. (ENT: "Desert Crossing")

A year later, a group of five adolescent drones, the last survivors of the crew of a Borg cube, utilized a dispersal field to mask their approach to the Delta Flyer. This left the crew of the Flyer unaware of the cube's approach until it was in visual range. (VOY: "Collective")